Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by the# » Tue, 15 May 2001 18:44:52



Does anybody know if the common 3000mah NimH packs on the market can compete
with the Sanyo RC2400 racing cells for 20-30 amp discharges?  I'm talking
sustained voltage, for a ducted fan jet.  Does anybody know what common
Li-Ion cells like those found in some cell phone batts can handle for
discharge?  3x the runtime, if you've got the space for the cells.

Anyway, for a 20-30 amp jet motor, should I go with the 3000mah NimH, or the
2400mah NiCd?

Any help is always much appreciated!

-oh, and by the way greg, just you wait 'till I build my slingshot launcher,
so I can actually get a chance to obtain control of my aircraft 8-}

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Jonny Hodgso » Wed, 16 May 2001 03:27:07



Quote:
> Does anybody know if the common 3000mah NimH packs on the market can
compete
> with the Sanyo RC2400 racing cells for 20-30 amp discharges?  I'm talking
> sustained voltage, for a ducted fan jet.  Does anybody know what common
> Li-Ion cells like those found in some cell phone batts can handle for
> discharge?  3x the runtime, if you've got the space for the cells.

> Anyway, for a 20-30 amp jet motor, should I go with the 3000mah NimH, or
the
> 2400mah NiCd?

A constant current draw of that size matches our average current pretty
well,
so I'd say the 3000s will cope - especially since you won't be pulling the
high peak currents.

I *believe* that Li-ion are not suited to high-current applications, but I
don't
know where the cutoff is...

Jonny

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Tom » Wed, 16 May 2001 08:17:43


Quote:

> Does anybody know if the common 3000mah NimH packs on the market can compete
> with the Sanyo RC2400 racing cells for 20-30 amp discharges?  I'm talking
> sustained voltage, for a ducted fan jet.  Does anybody know what common
> Li-Ion cells like those found in some cell phone batts can handle for
> discharge?  3x the runtime, if you've got the space for the cells.

> Anyway, for a 20-30 amp jet motor, should I go with the 3000mah NimH, or the
> 2400mah NiCd?

NiCad is much better suited for high discharge rates than any of the other
mentioned cell chemistries.  Although people use NiMH for high sustained
discharge rates, the cycle life is very poor in comparison to NiCad.

___
TTTTT   OO   M   M The sixth sick shiek's sixth sheep's sick.   |~~~|

  T    O  O  M M M So if it is in it or if it is on it, it is     *  
  T     OO   M   M        as it is, be it in it or on it.        `-'

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Rod McRa » Wed, 16 May 2001 09:33:59


NiMH 3000's will handle that current draw very well. They do take longer to
recharge, partly a consequence of their greater capacity. You will get
significantly longer runs from the 3000 NiMH cells than from the 2400
Nicads. I have been using both for some time, NiMH for 2 years and the 2400
Nicads for 1 year.

--
Rod McRae


Quote:

> > Does anybody know if the common 3000mah NimH packs on the market can
compete
> > with the Sanyo RC2400 racing cells for 20-30 amp discharges?  I'm
talking
> > sustained voltage, for a ducted fan jet.  Does anybody know what common
> > Li-Ion cells like those found in some cell phone batts can handle for
> > discharge?  3x the runtime, if you've got the space for the cells.

> > Anyway, for a 20-30 amp jet motor, should I go with the 3000mah NimH, or
the
> > 2400mah NiCd?

> NiCad is much better suited for high discharge rates than any of the other
> mentioned cell chemistries.  Although people use NiMH for high sustained
> discharge rates, the cycle life is very poor in comparison to NiCad.

> ___
> TTTTT   OO   M   M The sixth sick shiek's sixth sheep's sick.   |~~~|

>   T    O  O  M M M So if it is in it or if it is on it, it is     *
>   T     OO   M   M        as it is, be it in it or on it.        `-'

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by matthe » Wed, 16 May 2001 23:25:16



Quote:
> NiMH 3000's will handle that current draw very well. They do take longer
to
> recharge, partly a consequence of their greater capacity. You will get
> significantly longer runs from the 3000 NiMH cells than from the 2400
> Nicads. I have been using both for some time, NiMH for 2 years and the
2400
> Nicads for 1 year.

The crossover point (the point where the capacity is reduced to about 2400
mah, therefore equaling the Sanyo NiCad) for Panasonic cells is about 20A,
and for Sanyo cells 30A. Over these currents the Sanyo NiCd cells actually
have greater capacity.

They take a long time to charge because they have an exothermic reaction on
charging, and get hot right away. You can charge Nicad cells at 5A easily.
Stick to 1A for the NiMh cells.

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Rod McRa » Thu, 17 May 2001 00:49:30



rate or 3 amps in the case of the 3000 NiMH cells. I use the 1C charge rate
regularly and have done so for the past 2 years.

--
Rod McRae


Quote:



> > NiMH 3000's will handle that current draw very well. They do take longer
> to
> > recharge, partly a consequence of their greater capacity. You will get
> > significantly longer runs from the 3000 NiMH cells than from the 2400
> > Nicads. I have been using both for some time, NiMH for 2 years and the
> 2400
> > Nicads for 1 year.

> The crossover point (the point where the capacity is reduced to about 2400
> mah, therefore equaling the Sanyo NiCad) for Panasonic cells is about 20A,
> and for Sanyo cells 30A. Over these currents the Sanyo NiCd cells actually
> have greater capacity.

> They take a long time to charge because they have an exothermic reaction
on
> charging, and get hot right away. You can charge Nicad cells at 5A easily.
> Stick to 1A for the NiMh cells.

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Mark S. Jenning » Thu, 17 May 2001 02:32:01


Quote:
> They take a long time to charge because they have an exothermic reaction
on
> charging, and get hot right away. You can charge Nicad cells at 5A easily.
> Stick to 1A for the NiMh cells.

Panasonic specifically recommends 3-4 A right on the packaging of their 3000
cell packs.

FWIIW, I charge my NiMh 3000's at 1C (3.0A) and my 1500-2000 NiCads at 3C
(4.5A) without any problems.  The NiMh's have had perhaps 50 cycles and
still show the same capacity as new.  You do need a charger that can handle
the smaller delta-V peak.

- Mark

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Jonny Hodgso » Thu, 17 May 2001 21:11:52



Quote:
> The crossover point (the point where the capacity is reduced to about 2400
> mah, therefore equaling the Sanyo NiCad) for Panasonic cells is about 20A,
> and for Sanyo cells 30A. Over these currents the Sanyo NiCd cells actually
> have greater capacity.

Interesting information!  So, how come we model car racers see noticeably
longer run-times with 3000s (as well as, allegedly, more punch...)?

Jonny

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by matthe » Fri, 18 May 2001 07:57:37


Quote:
> Interesting information!  So, how come we model car racers see noticeably
> longer run-times with 3000s (as well as, allegedly, more punch...)?

cognitive dissonance.

Have you seen "more punch"? vs. a Sanyo RC 2400 NiCad?

the batteries have a higher internal resistance, and the voltage will be lower
at a given current, hence less power. One can compensate by gearing for higher
currents.

Most car motors die (slow death) at 35A (actually, the armatures remagnetize the
magnets backwards, killing them)

i.e.., you don't run high currents

Steve Neu did a careful analysis with constant load lab equipment, and lab data
acquiring equipment. You can read about it in Sailplane and Electric Modeler.

btw, the Sanyos are significantly better than Panasonics.

--
Matthew Orme
Microsoft "Where do you want to go today? It doesn't matter, you're coming with
us."
for answers to your electric questions, sign up for the eflight list at
http://www.ezonemag.com

 
 
 

Batteries: NimH vs. NiCD which is better for 20+amp jet motor?

Post by Jonny Hodgso » Fri, 18 May 2001 17:02:51



Quote:
> > Interesting information!  So, how come we model car racers see
noticeably
> > longer run-times with 3000s (as well as, allegedly, more punch...)?

> cognitive dissonance.

> Have you seen "more punch"? vs. a Sanyo RC 2400 NiCad?

I haven't run either, but I've heard that Sanyo 3ks are better than
*most* 2-4s - there are supposed to be a couple of "good batches"
of 2-4s but the rest are less impressive.

Quote:
> the batteries have a higher internal resistance, and the voltage will be
lower
> at a given current, hence less power. One can compensate by gearing for
higher
> currents.

Do you have a source on IR figures for both?  I'd be interested...

Quote:
> Most car motors die (slow death) at 35A (actually, the armatures
remagnetize the
> magnets backwards, killing them)

> i.e.., you don't run high currents

<shrug> That depends entirely on your definition of "high current".  My
physics teacher used to reckon an amp was large; the electric shunting
truck I worked on a couple of years ago maxed out around 600A.

We dump 2ks in five minutes, which is in excess of a 20A average,
and since we're off the power for significant parts of a lap I'd imagine
that peaks are rather higher.  Assuming my speedo's calibrated okay,
I used to find that setting the current limit below 40A gave a large
drop in torque out of corners.

Quote:
> Steve Neu did a careful analysis with constant load lab equipment, and lab
data
> acquiring equipment. You can read about it in Sailplane and Electric

Modeler.

From the spelling, I take it that's an American magazine...

Quote:
> btw, the Sanyos are significantly better than Panasonics.

What about the Powers cells?

Jonny